Generally, a light-emitting element does not require an external light source, and has a function light emitting by itself. Especially, it has advantages such as a high light-emitting efficiency, excellent luminance and viewing angle, and a quick response speed, but it has a disadvantage that its life is shortened because water or oxygen in the atmosphere is introduced inside the light-emitting element so that electrode is oxidized or a deterioration of element itself is progressed. For this reason, various studies are being carried out to manufacture a light-emitting element that is stable about water and oxygen.
Meanwhile, an organic EL element has a problem that when operating the organic EL element for a certain period, a light-emitting property, such as a light-emitting luminance, a light-emitting efficiency, and a light-emitting uniformity is significantly deteriorated as compared with an initial stage. For example, a cause of deterioration of the light-emitting properties as mentioned above includes an oxidation of electrode due to oxygen permeated inside the organic EL element, an oxidative degradation of organic material caused by a heat during operation, and a denaturalization of organic material. Also, a cause of deterioration of the light-emitting properties further includes a mechanical deterioration of constitution, and for example an interface delaminating of constitution is caused by water and oxygen, and also is generated by causing stress generation on an interface of constitution due to the heat generation and high temperature atmosphere during operation because of a difference between the coefficients of thermal expansion of each constituent.
In order to prevent the above problems, various technologies to seal the organic EL element for suppressing the contact with water and oxygen are researched. For example, as shown in FIG. 1, there is a method for preventing a reaching of water to the organic EL element, comprising: placing a sealing cap 2, in which an absorbent 6 adheres to an inner wall, on a picture element area having an organic EL element including a substrate 1, and a transparent electrode 3, an organic functional layer 4, and a metal cathode electrode 5 formed on the substrate 1; filling a nitrogen gas 9 inside it; and fixing the sealing cap to the substrate 1 by using an adhesive 7.
At this time, various materials are being researched as the absorbent, but alkaline earth metal oxides, such barium oxide (BaO) or calcium oxide (CaO) are widely researched because they can surely capture water molecular and also cannot release water molecular at high temperature not like a water absorbent, such as silica gel or zeolite, that absorbs physically water.
However, the water absorbents have disadvantages that they are particles of an inorganic compound, and require a concave substrate for adhering inside the element so that the element manufactured thickens. Furthermore, the alkaline earth metal oxides are opaque so that it can be applied to a so-called bottom light-emitting display element that emits display light to the substrate 1. However, when the alkaline earth metal oxides are applied to a so-called upper light-emitting display element that emits display light to the sealing cap 2 that is the other side of the substrate 1, a light-emitting can be blocked by the absorbent 6 so that the absorbent 6 should be located to be not entered to an image picture area and the installation place should be provided.
In order to apply the absorbent to the upper light-emitting display element, for example, it can be easily considered that a polymer, such as polyvinyl alcohol and nylon that are transparent and have a property for absorbing water is used as the absorbent. However, the polymer as mentioned above absorbs physically water, and does not have a sufficient water absorbing property as mentioned above.
Furthermore, Japanese Publication Patent No. 2001-357973 discloses using particulate water absorbent that is located to not affect adversely to the light transmission property in the upper light-emitting structure, and Japanese Publication Patent No. 2002-56970 discloses using a plastic substrate having a distributed water absorbents, of which the particle size is smaller than the light emitting wavelength of the organic EL element. However, the inorganic particles are difficult to arrange and evenly distribute as a first particle so that the decrease of the transmittance due to the light scattering cannot be avoided.
In addition, the absorbent produced using the compound synthesized by using an active solvent, such as toluene has a disadvantage that it is left in an optical element in small quantity so that the light emitting property is hindered by causing the phenomenon, such as dark spot, shrinkage, and the like.